Generally, a thermoplastic polyester, for example, polyethylene terephthalate (PET), has excellent mechanical properties and chemical properties, and is used broadly as formed products such as films or fibers.
However, there is a problem that the productivity deteriorates by the poor running ability when a polyester is processed into formed products. As a method for improving such a problem, a method for dispersing particles in a polyester and providing protrusions on the surface of a formed product has been performed. Although this method is effective to solve the problem on running ability, abrasion resistance and scratch resistance of a formed product cannot be improved to satisfactory levels.
Further, in a case where a formed product, for example, a film for a magnetic tape, is low in abrasion resistance, powder abraded from the film is likely to be generated in a process for manufacturing the magnetic tape, missing of coating is liable to occur in a magnetic-layer coating process, and as a result, missing of magnetic recording (drop out) is liable to occur. In a case of using a magnetic tape, because the tape is run contact with various devices such as a recording.cndot.regenerating device in most cases, abraded powder caused by the contact adheres onto the magnetic tape, thereby causing missing of magnetic recording (drop out) at the time of recording or regenerating.
Namely, in a film for a magnetic tape, running ability and abrasion resistance are required both in a manufacturing process of a magnetic tape and in using as a magnetic tape.
To solve the above-described problems, a method for adding external particles (external particle method) and a method for precipitating particles by a residue of a catalyst (internally formed particle method) have been investigated. For example, as such an external particle method, JP-A-SHO 62-172031 (addition of silicone particles), JP-A-HEI 5-3377 (addition of spherical silica and calcium carbonate particles), JP-A-HEI 5-4412 (addition of spherical silica particles), JP-A-HEI 5-4413 (addition of spherical silica particles), and a method disclosed in JP-B-HEI 7-45576 are raised. However, the particles used in these methods are poor in affinity with PET, and they frequently fall off and cause trouble. Further, addition of specified aluminum silicate particles is proposed in JP-A-SHO 55-45118, JP-A-SHO 55-107495, JP-A-HEI 4-220447, JP-A-HEI 3-25451 and JP-A-HEI 6-329884. In the former two disclosures, however, the shape of the particles is undefined, there are many excessively large particles in the particle size distribution, and they are still insufficient in surface evenness and abrasion resistance. In the latter three disclosures, there remain some matters to be improved such as matters that the particle size distribution is broad and that the thermal resistance is low when formed into a polyester composition.
As for internally formed particle, methods disclosed in JP-A-SHO 34-5144 (containing an alkali metal salt), JP-A-SHO 40-3291 (containing a terephthalic salt), JP-A-SHO 48-61556 (containing lithium element) and JP-A-SHO 51-112860 (containing lithium element, calcium element and phosphorus element) are proposed. However, although it is known that these internally formed particles can make particular surface protrusions, the surface protrusions are relatively soft and are likely to be damaged as compared with external particle methods, and therefore, there are some matters to be improved in these methods.
Recently, higher quality has been required for uses as films, and a raw material for films having a higher function is desired to be developed. In products produced from the conventional raw materials, running ability and abrasion resistance are not sufficient, and a further improvement is required.